In lighting applications, phosphors can be used to modify the wavelength of the light output. For example, a light emitting diode (LED) lighting device typically consists of a LED chip (“LED”) and a phosphor or a blend of phosphors. The chip emits the primary light with higher photon energy while the phosphor emits a light with lower photon energy upon the excitation of the primary light. The phosphors can be used to modify the wavelength of the primary light. For example, with certain phosphors the emission of an ultraviolet (UV) or blue LED can be modified to produce other visible lights by positioning the phosphors along the emission pathway to convert the primary light to longer wavelengths. An appropriate blend of blue-, green- and red-emitting phosphors can be used to modify UV LED emission to white light (i.e., light of white chromaticity). Certain combinations of green- and red-emitting phosphors can be used to modify a blue output of a LED to white light. Yellow emitting phosphors can be mixed with light from a blue LED or a blue emitting phosphor to create light of white chromaticity. Light from other UV or blue emitting devices, such as fluorescent lamps, can be similarly modified by the phosphors. The phosphor described here, when matched with appropriate other light sources, can be used in such applications.
The phosphors of the present invention are comprised of at least one halosilicate, also called silicate halide, as a host crystal and certain transition metal ions and rare earth metal ions as activators. The halosilicate is a class of crystals in which both the silicate group and a halide ion are defining elements in determining the crystal structure. For example, the crystal Ca2SiO4CaCl2 (see, e.g., V. R. Czaya and G. Bissert, Acta Cryst. B27, 747(1971)), Ca2SiO3Cl2 (see, e.g., N. I. Golovastikov and V. F. Kazak, Sov. Phys Crystallogr., 22(5), 549 (1977)) and Sr2LiSiO4F (see, e.g., A. Akella and D. Keszler, Chem. Mater. 7, 1299, (1995)) are typical halosilicates. In the crystals, the silicate group, e.g., [Si2O7]6− and [SiO4]4− and the halide ions, e.g., Cl− or F−, constitute the compound in a definite stoichiometry and determine the crystal structures. In contrast, there are phosphors that are comprised of silicates and halide ions, but the halide ions exist as dopant, which does not determine the crystal structure but may cause slight modifications, such as, causing expansions or contractions of the lattice. The dopant is present in quantities less than the major defining ions of the halosilicate.
Certain metal silicate halide phosphors have been described, though without describing their suitability for LED applications. See for example:
CrystalRef.FormulaλexλemStructureAkella and Keszler,Sr2LiSiO4F:Eu380520P21/m,Chem. Mater. 7: 1299monoclinic(1995)Burrus and Nicholson,Sr2Si3O8•2SrCl2:Eu410505Not ReportedJ. Lumin. 3: 467 (1971)(NR)U.S. Pat. No. 3,790,490Sr5Si4O10Cl6:Eu, Mn370greenNR(Datta et al.)(1974)Burrus and NicholsonSr4Si3O8Cl2:EuNRNRNR(1971)Burrus and NicholsonCa3SiO4Cl2:Eu (or370515 brdP21/m,(1971);Pb2+ or othermonoclinicactivator candidates)GB 1,414,381 (King etal.) (1973);Wanmaker and Verriet,Philips Res. Repts. 28:80 (1973)Garcia et al., J.Ba5SiO4Cl6:Eu410440monoclinic,Electrochem. Soc.,Cc126(10): 1734 (1979)Garcia et al., J.Ba7Si2O7Cl8:Eu420Y-GrnNRElectrochem. Soc.,126(10): 1734 (1979)Garcia et al., J.Ba5Si2O6Cl6:Eu420Y-GrnNRElectrochem. Soc.,126(10): 1734 (1979)
These crystalline materials have been synthesized and their crystal structures have been determined by X-ray diffraction. Certain transition metal ions and rare earth metal ions can be doped as luminescent activators in these crystals.
Certain metal silicate halide minerals (non-phosphors) have been described. See for example:
Ref.FormulaA. Winkler, et al, Z. Anorg.Sr5SiO4Cl6Allg. Chem, 504, 89, (1983)A. Winkler, et al. (1983).Sr5Si2O7Cl4A. Winkler, et al. (1983).Sr8Si4O12Cl8A. Winkler, et al, Z. Anorg.Ba7Si2O7Br8Allg. Chem, 542, 131, (1986)A. Winkler, et al. (1986).Ba15Si6O18ClA phosphor comprising these crystals has not been reported.
Thus, the present invention is directed to novel halosilicate phosphors and uses thereof in lighting devices including LED-containing lighting devices.